Recording/reproducing method of magnetic tape

ABSTRACT

In a recording/reproducing method of a magnetic tape in a tracking servo system, a recording density of each data track is increased while inhibiting occurrence of a recording/reproducing error caused by a size change of a magnetic tape in the width direction. Data tracks are each set to have a smaller track width stepwise as closer to servo tracks ( 41 T- 1  to  41 T- 5  etc.) in the width direction of a magnetic tape  1.  With such a setting, the width of the data tracks (A 1 - 41 T- 1  to A 1 - 41 T- 5  etc.) closest to the servo tracks ( 41 T- 1  to  41 T- 5 ) can be minimized, thereby enabling a significant increase in number of the data tracks. Further, even when the size of the magnetic tape  1  changes in the width direction due to a change in external environment such as a temperature or moisture, to lead to large displacement of the data tracks (A 8 - 41 T- 1  to A 8 - 41 T- 5 ) distant from the servo tracks ( 41 T- 1  to  41 T- 5 ), the data head (A 8 ) can be readily aligned to face the data tracks (A 8 - 41 T- 1  to A 8 - 41 T- 5 ) in the reproduction by an increased portion of the width size of the data tracks (A 8 - 41 T- 1  to A 8 - 41 T- 5 ), and it is thereby possible to ensure reading of data signals from the data tracks (A 8 - 41 T- 1  to A 8 - 41 T- 5 ) so as to improve reproduction accuracy.

This application is a Divisional of co-pending application Ser. No.11/129,400, filed on May 16, 2005, the entire contents of which arehereby incorporated by reference and for which priority is claimed under35 U.S.C. § 120.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a recording/reproducing method of amagnetic tape in a tracking servo system, using a multi-channel typehead unit comprising a plurality of data heads forrecording/reproduction.

2. Description of the Related Art

There are a variety of uses of a magnetic tape, including uses as anaudio tape, a video tape and a computer tape. Particularly in the fieldof computer data backup tapes, a recording capacity has been increasedwith increase in capacity of a hard disc as a backup target. One ofmeans for increasing the capacity of a magnetic tape is narrowing thewidth of each data track to increase the number of the data tracks, theso-called increase in recording density of data tracks.

In increasing a recording density of data tracks, it is essential tointroduce a recording/reproducing technique named a so-called trackingservo system. The tracking servo system here refers to a technique inwhich servo tracks consisting of servo signals previously written on amagnetic tape are read with servo heads provided on a head unit, and inresponse to the read signals, the positional shift of the head unit inthe width direction of the magnetic tape is controlled, to allow dataheads to follow corresponding data tracks. According to this trackingservo system, even when the magnetic tape vibrates in the widthdirection in recording/reproduction to lead to displacement of the datatracks, the vibration of the magnetic tape is detected from changes insignals of the servo heads which are tracking signals from the servotracks, and according to these changes, recording heads can be led ontothe data tracks, thereby enabling significant improvement inrecording/reproduction accuracy.

Conventional examples of such a tracking servo system are described inJapanese Laid-Open Patent Publication No. 2002-157722, JapaneseLaid-Open Patent Publication No. 2003-173508, and the like. In JapaneseLaid-Open Patent Publication No. 2002-157722, in addition to normalservo heads, pre-reading servo heads are provided for reading positionalinformation of servo tracks prior to reading by the normal servo headsso that tracking servo accuracy can be improved. In Japanese Laid-OpenPatent Publication No. 2003-173508, a servo signal for fine movementwritten in each data track on a magnetic tape is read with a magnetichead, and based upon the read signal, an actuator for fine movementbuilt in each magnetic head is driven to control fine movements of arecording head and a reproducing head individually, so that trackingservo accuracy can be improved.

SUMMARY OF THE INVENTION

One example of recording/reproducing methods of a magnetic tape in thetracking servo system is more specifically described using FIG. 4. Ahead unit 2 used in this example comprises two head groups: a head group31 consisting of eight data heads (A1 to A8) which form data tracks(A1-41T-1 etc.) in data track regions (3-1 etc.: FIG. 1 according to thepresent invention) of a magnetic tape 1 (FIG. 1) when the magnetic tape1 travels forwardly from the beginning side to the end side; and a headgroup 32 consisting of eight data heads (B1 to B8) which form datatracks (B1-42T-1 etc.) when the magnetic tape 1 travels backwardly fromthe end side to the beginning side. At the respective end parts of thehead groups 31 and 32 in the width direction (Y direction) of themagnetic tape 1, servo heads 41 and 42 are provided for tracing theservo tracks (41T-1 to 41T-4, 42T-1 to 42T-4 etc.) previously formed onthe magnetic tape 1.

In each of the data heads (A1 to A8, B1 to B8) built are a recoding headfor writing a data signal to form a data track and a reproducing headfor reading the data signal from the data track. In a typicalconfiguration, the track width size of the recording head is set largerthan that of the reproducing head. In other words, the track width ofthe reproducing head is set smaller than the track width of the datatrack (A1-41T-1 etc.) to be formed with the recording head. Therefore,if relative positions between the data tracks and the reproducing headsfall within this margin in the reproduction, the operation of readingdata from the data tracks can be performed without trouble.

Using the head unit 2 as thus described, first, a servo track (41T-1) istraced with the servo head 41 and, while performing tracking servo, datatracks are written with the data heads (A1 to A8) on the forwardtraveling magnetic tape 1. In the illustrated example, data tracksformed in such a writing/recording operation are denoted as (A1-41T-1)to (A8-41T-1).

When the magnetic tape 1 reaches the end, a switch is made to the dataheads (B1 to B8). The servo track 42T is then traced with the servo head42 and, while performing tracking servo, data tracks (B1-42T-1) to(B8-42T-1) are written. In forming the data tracks (B1-42T-1) to(B8-42T-1), the head unit 2 is shifted in the width direction (Ydirection) of the magnetic tape 1 so as to prevent these data tracks(B1-42T-1) to (B8-42T-1) from overlapping the data tracks (A1-41T-1) to(A8-41T-1) formed in the previous forward traveling. When the magnetictape 1 reaches the beginning, a switch is made back to the data heads(A1 to A8). The head unit 2 is then shifted to trace the servo track(41T-2) with the servo head 42 and, while performing tracking servo, thedata tracks (A1-41T-2) to (A8-41T-2) are formed. Further, when themagnetic tape 1 reaches the end, a switch is made to the data heads (B1to B8). The head unit 2 is then shifted to trace the servo track (42T-2)with the servo head 42 and, while performing tracking servo, the datatracks (B1-42T-2) to (B8-42T-2) are formed. In the present example,writing in a data track region (3-1) is completed by repetition of theoperation as thus described four times, and thereafter, the head unit 2is greatly moved to a succeeding data track region (3-2), and forms datatracks in this data track region (3-2).

The reproducing operation is performed in a procedure inverse to theprocedure of the previously performed recoding operation. Namely, theservo tracks (41T-1 etc.) are traced and, while performing trackingservo, the data heads (A1 to A8, B1 to B8) are aligned to face thecorresponding data tracks. Thereafter, data signals written in the datatracks are read with the reproducing heads in the data heads (A1 to A8,B1 to B8).

In the conventional figuration as thus described, all the data heads (A1to A8, B1 to B8) are set to have the same size in the width direction (Ydirection) of the magnetic tape 1, and hence all the track width of thedata tracks are set to have the same width. The smaller the track widthof each of the data tracks, the larger the number of data tracks on amagnetic tape can be. This is an advantage in increasing the recordingcapacity of the magnetic tape. In the meantime, however, a differencemay occur in expansion coefficient between the magnetic tape 1 and thehead unit 2 due to a change in tracking servo accuracy or a change inexternal environment such as a temperature or moisture, thereby makingthe sizes of the magnetic tape 1 and the head unit 2 different, or thewidth of the magnetic tape 1 may change caused by leaving the tapeunused after taken up. In view of these problems and the like, the lowerlimit value of the data track width is determined by itself. If thetrack width of each of the data tracks is as small as below this lowerlimit value, the data heads are more likely to be displaced from thedata tracks to cause unstable data reading, thereby increasing an errorrate.

Among the foregoing problems that cause the displacement of the relativeposition between the data track ad the data head, the vibration of thetape in the width direction in the traveling can be dealt with byimprovement in tacking servo performance, whereas the other problems,like the problem of the size difference between the head unit and themagnetic tape caused by the difference in expansion coefficienttherebetween due to a temperature or moisture change and the problem ofthe change in tape width caused by leaving the tape unused after takenup, cannot be dealt with by improvement in tracking servo performance.Namely, the reproduction accuracy may be lowered, as displacement, whichoccurs due to an external environmental change or the like, between thedistance from the servo head 41 or 42 on the head unit 2 to the datahead (A8, B1) located most distant from the servo head 41 or 42 and thecorresponding distance from the servo tracks (41T-1 to 41T-4, 42T-1 to42T-4) to the data tracks (A8-41T-1 to A8-41T-4, B1-42T-1 to B1-42T-4)becomes not ignorable relative to the foregoing margin.

A specific example is described below. When the distance from the servohead 41 or 42 to the data head A8 or B1 located most distant from theservo head 41 or 42 is 250 μm, and the respective track widths of therecording head and the reproducing head in the data head A8 or B1 are 20μm and 12 μm, a displacement margin of one side of the reproducing headis as small as 4 μm. Since the expansion change of the head unit 2 andthat of the magnetic tape 1 in the width direction due to a temperatureor moisture change depend largely upon a moisture difference, a moistureexpansion coefficient is used in the following consideration. In thecase where the magnetic tape 1 has a moisture expansion coefficient of2×10⁻⁵/% RH, when the moisture changes by 40% RH from the time ofrecording to the time or reproduction, a displacement of 2.0 μm at themaximum occurs in the figuration shown in FIG. 4 described above.Therefore, in the data track located closest to the servo track, thevibration of the magnetic tape 1 in the width direction in the travelingcauses no problem up to a vibration amplitude of about 8 μm, whereas inthe data track located most distant from the servo track, an allowablevibration amplitude range is as small as 4 μm, and thereby reading ofdata from this track tends to be unstable. This may become a big,inevitable problem in an attempt to increase the recording density ofthe data tracks for the purpose of further increasing the capacity ofthe magnetic tape.

Such a problem can be solved by individual control of fine movements ofthe recording head and the reproducing head in each of the magneticheads based upon servo signal for fine movement written in each of thedata tracks on the magnetic tape, as described in above-mentionedJapanese Laid-Open Patent Publication No. 2003-173508. However, in themethod according to this document, since the servo signals for finemovement are written in the data tracks on the magnetic tape, it isimpossible to avoid reduction in data recording area by the region ofthe servo signals for fine movement, thereby inhibiting the increase inrecording density. Especially, this method has a disadvantage in thatthe configurations of the magnetic tape and the head unit are complex,and hence the control thereof also becomes complex.

An object of the present invention is surely preventing, with a simpleconfiguration, occurrence of a recording/reproducing error caused by asize change of a magnetic tape in the width direction, in arecording/reproducing method of a magnetic tape in a tracking servosystem. Another object of the present invention is increasing the numberof data tracks formed by writing on the magnetic tape to increase therecording density of the data tracks so as to obtain a magnetic tapewith high capacity.

As shown in FIGS. 1 to 3, the present invention is arecording/reproducing method of a magnetic tape 1, using a multi-channeltype head unit 2 comprising: a plurality of data heads (A1 to A8, B1 toB8) for recording/reproduction which form data tracks (A1-41T-1 etc.) onthe magnetic tape 1 and read data signals from the data tracks; andservo heads (41, 42) for tracing servo tracks (41T-1 to 41T-5, 42T-1 to42T-5, etc.) previously provided on the magnetic tape 1, the methodcomprising: a recording process for forming a plurality of data tracks(A1-41T-1 etc.) on the magnetic tape 1 with the data heads (A1 to A8, B1to B8) while tracing the servo tracks (41T-1 to 41T-5, 42T-1 to 42T-5,etc.) on the magnetic tape 1 with the servo heads (41, 42); and areproducing process for tracing the servo tracks (41T-1 to 41T-5, 42T-1to 42T-5, etc.) to read data signals recorded in the data tracks(A1-41T-1 etc.) while aligning the data heads (A1 to A8, B1 to B8) toface the data tracks (A1-41T-1 etc.)

The recording/reproducing method of a magnetic tape of the presentinvention is characterized in that the plurality of data tracks(A1-41T-1 to A8-41T-1 etc.) formed in the recording process are each setto have a smaller track width stepwise as located closer to the servotracks (41T-1 to 41T-5 etc.) in the width direction (Y direction) of themagnetic tape 1.

Namely, when taking a look at data tracks formed based upon the servotrack (41T-1), the data track (A8-41T-1) located most distant from theservo track (41T-1) is set to have the largest rack width. The otherdata tracks are each set to have a smaller track width stepwise aslocated closer to the servo track (41T-1) in the width direction (Ydirection) of the magnetic tape 1. The data track (A1-41T-1) locatedclosest to the servo track (41T-1) is set to have the smallest trackwidth. The term “stepwise” in the present invention represents a conceptincluding a figuration in which data tracks having the same track widthare aligned in one location or a plurality of locations, that is, threeor more data tracks are aligned and the data track located closest tothe servo track has the smallest track width while the data tracklocated most distant from the servo track has the largest track width,and the data track located between those two data tracks has a width ofan intermediate value between the largest and the smallest widths. Theconcept may also include a figuration in which, for example, the datatracks (A1-41T-1) and (A2-41T-1) are set to have the same track widthwhile the data track (A3-41T-1) and the other data tracks are each setto have a larger track width as located more distant from the servotrack.

More specifically, servo track regions (41T to 45T), each comprising aplurality of servo tracks (41T-1 etc.) traveling in the longitudinaldirection of the magnetic tape 1, are formed at prescribed intervals inthe width direction of the magnetic tape 1. Regions sectioned with theservo track regions (41T to 45T) in the width direction of the magnetictape 1 serve as data track regions (3-1 to 3-4) in which the data tracks(A1-41T-1 etc.) are formed. In the recording process, a recordingoperation is performed in the data track regions (3-1 to 3-4), not onlyin forward traveling of the magnetic tape 1, but in backward travelingof the magnetic tape 1 in the reverse direction to the forwardtraveling. In the data track regions (3-1 to 3-4), data tracks (A1-41T-1etc.) are formed so as to be alternately laminated in the widthdirection of the magnetic tape 1 in the forward/backward traveling.

In the forward traveling, the recording operation is performed usingservo tracks (e.g. 41T-1 to 41T-5) in the servo track region (e.g., 41T)located on one end side of the data track regions (3-1 to 3-4) in thewidth direction of the magnetic tape 1, whereas in the backwardtraveling, the recording operation is performed using servo tracks (e.g.42T-1 to 42T-5) in the servo track region (e.g., 42T) located on theother end side of the data track regions (3-1 to 3-4) in the widthdirection of the magnetic tape 1. Further, the plurality of data tracks(A1-41T-1 etc.) formed in the forward/backward traveling can each be setto have a smaller track width stepwise as located closer to the servotracks (41T-1 to 41T-5, 42T-1 to 42T-5) in the width direction (Ydirection) of the magnetic tape 1.

In the recording/reproducing method of a magnetic tape according to thepresent invention, the data tracks are each set to have a smaller trackwidth stepwise as located close to the servo tracks in the widthdirection (Y direction) of the magnetic tape 1, i.e. the data tracks areeach set to have a larger track width stepwise as located more distantfrom the servo track in the width direction (Y direction) of themagnetic tape 1. With this setting, the size of the magnetic tape 1changes in the width direction due to a change in external environmentsuch as a temperature or moisture. As a result, for example, even if thedata tracks (A8-41T-1 to A8-41T-5) located distant from the servo tracks(41T-1 to 41T-5) are greatly displaced, the data head (A8) can bereadily aligned to face the data tracks (A8-41T-1 to A8-41T-5) by anincreased portion of the track width size thereof. It is thereforepossible to ensure reading of data signals from the data tracks(A8-41T-1 to A8-41T-5) so as to improve reproduction accuracy. Further,the method according to the present invention has an advantage ofsimplicity of the whole configuration and easiness of control ascompared with the figuration for writing servo signals for fine movementas described in Japanese Laid-Open Patent Publication No. 2003-173508.

Additionally, since the track width of the data track closest to theservo track can be minimized, it is possible to significantly increasethe number of the data tracks to increase the recording density of thedata tracks, so as to contribute to an increase in capacity of themagnetic tape. In other words, for example, since the data tracks(A1-41T-1 to A1-41T-5) adjacent to the servo tracks (41T-1 to 41T-5) arehardly affected by a size change of the magnetic tape 1 in the widthdirection (Y direction) due to an external environmental change, thetrack width of the data tracks (A1-41T-1 to A1-41T-5) can be minimizedwithout impairing accuracy of reading of data signals from the datatracks (A1-41T-1 to A1-41T-5). Moreover, the track widths of the datatracks (A2-41T-1 to A2-41T-5 etc.) other than the data tracks (A1-41T-1to A1-41T-5), which are closer to rather than distant from the servotracks, can be made as small as possible in the range where the datatracks (A2-41T-1 to A2-41T-5 etc.) are not affected by the size changeof the magnetic tape 1 in the width direction. As thus described,according to the present invention, it is possible to significantlyincrease the number of the data tracks so as to increase the recordingdensity of the data tracks.

With the recording operation arranged to be performed in the data trackregions (3-1 to 3-4) not only in forward traveling of the magnetic tape1 but in backward traveling of the magnetic tape 1 in the reversedirection to the forward traveling, it is possible to increase therecording density of the data tracks. Further, if the plurality of datatracks (A1-41T-1 etc.) formed in the forward/backward traveling are eachset to have a larger track width stepwise as located distant from theservo tracks (41T, 42T), which were used for forming the data tracks(A1-41T-1 etc.), in the width direction of the magnetic tape 1, theinfluence of the size change of the magnetic tape 1 in the widthdirection, which occurred due to a change in external environment suchas a temperature or moisture, can be reduced and it is thereby possibleto ensure reading of data signals from the data tracks (A8-41T-1 toA8-41T-5, B1-42T-1 to B1-42T-5) so as to improve the reproductionaccuracy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing one example of a relationship between amagnetic tape and a head unit in a recording/reproducing method of amagnetic tape according to the present invention.

FIG. 2 is a plan view showing one example of a multi-channel type headunit.

FIG. 3 is a view of explaining relationships between the head unit anddata tracks to be written on the magnetic tape.

FIG. 4 is a view showing a conventional recording/reproducing method ofa magnetic tape.

FIG. 5 is a view showing a relationship between an increase in recordingcapacity and a value obtained by the minimum recording head trackwidth/the maximum recording head track width, in therecording/reproducing method of a magnetic tape according to the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 to 3 show one of embodiments of the recording/reproducing methodof a magnetic tape according to the present invention. It is to be notedthat the tracking servo system is classified into a magnetic servosystem (system where a servo signal is formed on a magnetic layer bymagnetic recording, which is magnetically read to perform servotracking) and an optical servo system (system where a servo signalconsisting of an array of recessed portions is formed on a back layer bylaser irradiation or the like, which is optically read to perform servotracking). While the idea of the present invention is applicable toeither of the two servo systems, in the present embodiment, the former,magnetic servo system is described as an example.

In FIG. 1, reference numeral 1 denotes a magnetic tape, and referencenumeral 2 denotes a head unit built in a tape drive. The head unit 2 canbe freely shifted and moved in the width direction of the magnetic tape1 by an actuator not shown in the figure, along an arm 6 extendingacross the width direction. The magnetic tape 1 is traveled and moved bymeans of a driving mechanism of the tape drive in a forward travelingdirection and in a backward traveling direction. The forward travelingdirection, indicated in the figure with a leftward arrow, is a directionin which the tape travels from the beginning to the end. The backwardtraveling direction, indicated in the figure with a rightward arrow, isa direction in which the tape travels from the end to the beginning. Itshould be noted that, in the following description, the forward/backwardtraveling direction of the magnetic tape 1 is appropriately referred toas an X direction and the width direction of the magnetic tape 1 as a Ydirection.

The head unit 2 is a multi-channel type head having a large number ofdata heads. As shown in FIG. 2, the head unit 2 comprises, on thesurface facing the magnetic tape 1, two servo heads 41 and 42, and thedata head groups 31 and 32 extending in two lines in the width direction(Y direction) of the magnetic tape 1. The data head groups 31 and 32each consist of eight data heads (A1 to A8, B1 to B8) disposed at equalintervals in the Y direction. Each of the data heads (A1 to A8, B1 toB8) comprises: a recording head which performs a writing operation onthe magnetic tape 1 to form data tracks (A1-41T-1 etc.: cf. FIG. 3); anda reproducing head which reads data from the data tracks (A1-41T-1etc.). The data head group 31 serves to perform recording/reproducingoperations in the forward traveling of the magnetic tape 1. The datahead group 32 serves to perform recording/reproducing operations in thebackward traveling of the magnetic tape 1. It is to be noted that, ineach of those data heads (A1 to A8, B1 to B8), the width size (trackwidth) of the reproducing head in the Y direction is set smaller thanthat of the recording head.

At the respective end parts of the data head groups 31 and 32 in thewidth direction (Y direction) of the magnetic tape 1, the servo heads 41and 42 are disposed. Namely, at the end part of the head group 31 forwriting in the Y direction in the forward traveling, the servo head 41is disposed for reading positional signals of the servo tracks (41T-1etc.: cf. FIG. 3) and tracing the servo tracks (41T-1 etc.) in theforward traveling. Meanwhile, at the end part of the other head group 32in the Y direction, the servo head 42 is provided for reading the servotracks (42T-1 etc.) in the backward traveling.

The magnetic tape 1 is a tape adapted to the recording/reproducingmethod in the tracking servo system. As shown in FIGS. 1 and 3, fiveservo track regions (41T to 45T) are juxtaposed at prescribed intervalsin the width direction (Y direction) of the magnetic tape 1. Each of theservo track regions (41T to 45T) consists of five servo tracks (41T-1 to41T-5, 42T-1 to 42T-5 etc.) traveling in the longitudinal direction overthe effective length of the magnetic tape 1. The surface region of themagnetic tape 1 is sectioned in the width direction with the servo trackregions (41T to 45T) into four data track regions (3-1 to 3-4). As shownin FIG. 3, in such data track regions (3-1 to 3-4), a large number ofdata tracks (A1-41T-1 to A1-41T-5: cf. FIG. 3) are formed in anafter-mentioned recording operation performed by the head unit 2. Itshould be noted that, although FIG. 3 shows the servo tracks (41T-1 to41T-5 etc.) and the data tracks (A1-41T-1 to A1-41T-5 etc.) displaced inthe horizontal direction, this is just for the sake of simplicity inexplanation. In practice, those tracks are formed over the longitudinaldirection of the magnetic tape 1.

The head unit 2 as thus configured performs a recording operation in theway of filling the spaces among the data heads (A1 to A8, B1 to B8), bybeing shifted by a prescribed width in every one-way traveling in such adegree that the data tracks are not overlapped with one another in thewidth direction (Y direction). More specific description is given below.First, the servo track (41T-1) is traced with the servo head 41 on themagnetic tape 1 traveling in the forward direction from the beginning tothe end and, while performing tracking servo, eight data tracks(A1-41T-1, A2-41T-1 to A8-41T-1) are written and formed with therecording heads built in the data heads (A1 to A8), constituting thehead group 31 for forward traveling recording/reproduction, in the datatrack region (3-1) of the magnetic tape 1.

Next, when the magnetic tape 1 reaches the end by means of the drivingmechanism on the tape drive side, a switch is made to the data heads (B1to B8) constituting the head group 32 for backward traveling. The servotrack (42T-1) is traced with the servo head 42 for backward travelingand, while performing tracking servo, eight data tracks (B1-42T-1,B2-42T-1 to B8-42T-1) are written with the data heads (B1 to B8). Thehead unit 2 is shifted in the width direction (Y direction) of themagnetic tape 1 to write the data tracks (B1-42T-1 to B8-42T-1) in sucha degree that these data tracks (B1-42T-1 to B8-42T-1) do not overlapthe data tracks (A1-41T-1 to A8-41T-1) formed in the previous forwardtraveling.

When the magnetic tape 1 reaches the beginning, a switch is made back tothe data heads (A1 to A8) constituting the head group 31 for the forwardtraveling. The head unit 2 is then shifted in the Y direction to tracethe servo track (41T-2) with the servo head 41 for the forward travelingand, while performing tracking servo, the data tracks (A1-41T-2,A2-41T-2 to A8-41T-2) are written with the data heads (A1 to A8). Whenthe magnetic tape 1 reaches the end, a switch is made back to the dataheads (B1 to B8) for the backward traveling. The head unit 2 is thenshifted in the Y direction to trace the servo track (42T-2) with theservo head 42 and, while performing tracking servo, the data tracks(B1-41T-2, B2-41T-2 to B8-41T-2) are written with the data heads (B1 toB8).

With writing of the data tracks (A1-41T-1 to B8-42T-5) completed afterrepetition of the above operation, writing in the data track region(3-1) is completed. The head unit 2 is then moved greatly onto asucceeding data track region (3-2), and performs the writing operationin this data track region (3-2). When performing the writing operationin the data track region (3-2), in the forward traveling, the servotracks (42T-1 to 42T-5) formed in the servo track region (42T) aretraced with the servo head 41 to perform tracking servo, and in thebackward traveling, the servo tracks formed in the track region (43T)are traced with the servo head 42 to perform tracking servo. The writingoperations are performed in the succeeding data track regions (3-3, 3-4)in exactly the same manner as in the previous data track regions.Accordingly, it is possible in the present embodiment to form a total of320 data tracks in the width direction (Y direction) of the magnetictape 1.

The reproducing operation can be performed in a procedure inverse to theprocedure in the previously performed recoding operation. Namely, theservo tracks (41T-1 etc.) formed in the servo track regions (41T to 45T)are traced to perform tracking servo, and the data heads (A1 to A8, B1to B8) are aligned to face the corresponding data tracks. Thereafter,data signals written in the data tracks are read with the reproducingheads in the data heads (A1 to A8, B1 to B8).

As thus described, when the recording/reproducing operations areperformed with the tracking servo system on the high recording densitytype magnetic tape 1 where a large number of data tracks are formed, asize change of the magnetic tape 1 in the width direction (Y direction),due to a change in external environment such as a temperature ormoisture, may appear as a large problem. That is, when the size of themagnetic tape 1 changes in the width direction (Y direction) under theinfluence of the external environmental change, the width sizes of theservo tracks and data tracks become larger/smaller, which might preventaccurate performance of the recording/reproducing operations.

The influence of such a size change is particularly conspicuous in thedata tracks located distant from the servo tracks. Since the size changeof the head unit 2 is hardly affected by an external environment, achange in distance from the servo head 41 or 42 to each of the dataheads (A1 to A8, B1 to B8) is considerably small as compared with thecase of the magnetic tape 1 even under the influence of the externalenvironment. On the other hand, when the size of the magnetic tape 1changes in the width direction (Y direction), a change in distance fromthe servo track to each of the data tracks is larger as the data trackis more distant from the servo track. Therefore, while the data tracks(e.g. A1-41T-1) located close to the servo track can be accurately read,the data heads (e.g. A8) cannot be accurately aligned to face thecorresponding data tracks (e.g. A8-41T-1) located distant from the servotrack, and hence reading of data signals from the data tracks locateddistant from the servo track becomes unstable, thereby tending toincrease an error rate.

In the present embodiment, as shown in FIG. 3, the data tracks are eachset to have a smaller track width stepwise as located closer to theservo tracks in the width direction (Y direction) of the magnetic tape1. With this configuration, even when the size of the magnetic tape 1changes in the width direction due to an external environmental changeto result in large displacement of, for example, the data tracks(A8-41T-1 to A8-41T-5) located distant from the servo tracks (41T-1 to41T-5), the reproducing head (A8) can be readily aligned to the datatracks (A8-41T-1 to A8-41T-5) by setting the width of the data trackmost distant from the servo track such that the positional relationshipsbetween the data tracks (A1-41T-1 to A1-41T-5) and the reproducing head(A8) fall within an allowable range, and it is thereby possible toensure reading of data signals from the data tracks (A8-41T-1 toA8-41T-5) so as to improve reproduction accuracy.

In order to obtain the action effect as thus described, as shown in FIG.2, the data heads (A1 to A8, B1 to B8) constituting the data head group31 or 32 are each set to have a smaller width size (t1 to t8) stepwiseas located closer to the servo head 41 or 42 in the width direction (Ydirection) of the magnetic tape 1. Therefore, as shown in FIG. 3, thedata tracks (e.g., A1-41T-1 to A1-41T-5 etc.) formed on the magnetictape 1 can each be set to have a smaller track width stepwise as locatedcloser to the corresponding servo tracks (e.g. 41T-1 to 41T-5 etc.) inthe width direction (Y direction) of the magnetic tape 1.

As described above, since each of the respective reproducing headsconstituting the data heads (A1 to A8, B1 to B8) is set to have asmaller width size in the width direction (Y direction) of the magnetictape 1 than the width size of the corresponding recording head, evenwhen the data tracks such as (A8-41T-1 to A8-41T-5) are displaced in thewidth direction (Y direction) of the magnetic tape 1, the reproducinghead can be readily aligned to face the data tracks (A8-41T-1 toA8-41T-5) by a portion of a difference in width size between therecording head and the reproducing head in the width direction (Ydirection), and it is thereby possible to favorably secure thereproduction accuracy. It should be noted that the term “width size” ofthe recording head or the reproducing head here means an effective widthof the head to contribute to writing or reading of data.

Additionally, in the figuration of the data tracks on the magnetic tape1 according to the present embodiment, the track width of the data trackclosest to the servo track can be minimized. Specifically, for example,the data tracks (A1-41T-1 to A1-41T-5) adjacent to the servo tracks(41T-1 to 41T-5) are hardly affected by a width size change of themagnetic tape 1 (Y direction) due to an external environmental change,and hence the track width of the data tracks (A1-41T-1 to A1-41T-5) canbe minimized without impairing accuracy of reading data signals from thedata tracks (A1-41T-1 to A1-41T-5). Moreover, the track widths of thedata tracks (A2-41T-1 to A2-41T-5 etc.) other than the data tracks(A1-41T-1 to A1-41T-5), which are close to rather than distant from theservo tracks, can be made as small as possible in the range where thedata tracks (A2-41T-1 to A2-41T-5 etc.) are not affected by the sizechange of the magnetic tape 1 in the width direction. With the widthsizes of the data tracks having made smaller as thus described, it ispossible to significantly increase the number of the data tracks toincrease the recording density of the data tracks, thereby largelycontributing to an increase in capacity of the magnetic tape. A specificexample is described as follows. In FIG. 4 illustrating the conventionalfiguration, the number of data tracks written in one data track regionis four, whereas in the present embodiment, the number of data tracksthat can be written in one data track region is five, which leads to anincrease in recording capacity by 25%.

According to the findings by the present inventor, a pitch (amount ofthe head unit shifted in either forward or backward traveling) betweenthe data tracks can be approximately set to a value obtained by: (themaximum recording head track width+the minimum recording head trackwidth)×½. It is thus possible to form a larger number of data tracks ascompared with the recording/reproducing figuration of a magnetic tape asshown in FIG. 4 as the conventional example, so as to increase therecording density. FIG. 5 shows a relationship between a capacityincrease and a value obtained by: the minimum recording head trackwidth/the maximum recording head track width. It is to be noted that inFIG. 5, the recording/reproducing figuration (the minimum width/themaximum width=1) in FIG. 4 as the conventional example is considered as100%. It is found from FIG. 5 that, when the value obtained by: theminimum width/the maximum width, is set to 0.5, the recording capacitycan be increased to 130%.

The maximum data track width and the minimum data track width aredetermined by specifications of a driving system, e.g. a distance from aservo head to a data head located most distant from the servo head, datahead mounting accuracy, a tension for taking up a magnetic tape,tracking servo accuracy and use environmental conditions. In theconventional recording method of a magnetic tape, there has been noother choice but to design a data track width as the herein-termedmaximum data track width. As opposed to this, according to the presentinvention, it is possible to set the data track width withoutrestriction by the above conditions, so as to surely obtain a systemwith a larger recording capacity than in the convention figuration.

The reproducing head is usually designed to have a smaller width thanthe width of the recording track. In the present invention, while thewidth of the reproducing head corresponding to the width of therecording head may be designed in the above-mentioned manner, it ispreferable to combine the reproducing head, having a smaller track widththan the minimum recording head track width, with every recording headso as to allow lower cost.

1. A recording/reproducing method of a magnetic tape, using amulti-channel type head unit comprising: a plurality of data heads forrecording/reproduction which form data tracks on the magnetic tape andread data signals from the data tracks; and servo heads for tracingservo tracks previously provided on the magnetic tape, wherein themethod comprises: a recording process for forming a plurality of datatracks on the magnetic tape with the data heads while tracing the servotracks on the magnetic tape with the servo heads; and a reproducingprocess for tracing the servo tracks to read data signals recorded inthe data tracks while aligning the data heads so as to face the datatracks, and the plurality of data tracks formed in the recording processare set to have a smaller track width stepwise as located closer to theservo tracks in the width direction of the magnetic tape, and datatracks having the same track width are aligned in one location or aplurality of locations.